1. Field of the Invention
The present invention generally relates to a sensor network, and more particularly to a method for detecting and avoiding external interference which can detect a channel interference, which may occur in the same network system or a different type network system using the same frequency band, by using an energy contour.
2. Description of the Related Art
Since frequency bands being currently used are shared by commercialized networks, such as a wireless LAN or Bluetooth®, they cannot avoid frequency interference, which may degrade communication speed or cause a network interruption. The same can be applied to a sensor network, and various studies for overcoming such interference are in progress.
The existing network interference avoiding technologies transmit a separate frame in order to detect the interference or overcome the interference problem between sensor nodes within a network by using a topology control. The separate frame is periodically transmitted in order to detect the interference, and the topology control refers to a method of avoiding the interference by controlling its own transmission power when interference from a network of the same type or a different type is detected. The method of controlling the topology is shown in FIG. 1.
FIG. 1 illustrates an example of a conventional method of avoiding interference between networks by using a topology control. As shown in FIG. 1, when interference from another network is detected, it is possible to avoid the interference by reducing the transmission power to a range capable of preventing the interference.
However, the existing methods as described above have several problems. First, in the method of transmitting a separate frame, since a separate frame is periodically and continuously transmitted in order to detect the interference, an energy loss due to the interference is inevitable.
Next, in the method of reducing the transmission power through topology control, other nodes that are not subjected to the interference may escape from the transmission range, and additional energy consumption may be necessary in order to connect the nodes escaping from the transmission range through another network. In other words, in the method of reducing the transmission power, although the problem of the nodes escaping from the transmission range can be solved by constructing a new topology, it is impossible to avoid an additional energy consumption due to the construction of a new topology and a communication interruption during the construction of the new topology. Moreover, the method of topology control cannot be a good solution in a Time Division Multiple Access (TDMA) system, which is sensitive to scheduling.
The technology of avoiding the interference by using the topology control cannot avoid interference from a different type network system using a different protocol. For example, in the case of a Radio Interference Detection (RID) algorithm, which is one of the interference detection algorithms in the Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 system, a transmission node sequentially broadcasts a High power Detection (HD) packet and a Normal power Detection (ND) packet, and a reception node can predict the degree of interference by detecting the transmission power difference between the HD packet and the ND packet. However, since this algorithm defines only the interference, which may occur between nodes using the IEEE 802.15.4 protocol, this algorithm is inevitably vulnerable to interference occurring between different types of networks. Further, since this algorithm also employs a transmission of a separate frame in order to detect the interference, it requires additional energy consumption for the transmission of a separate frame.
The methods described above do not take the mobility of a node or an interference source into account, while most of mobile terminals connected to a wireless Local Area Network (LAN) have a strong mobility. Therefore, there has been a necessity for a solution relating to this problem, but there is no sufficient study relating to this problem.